Heretofore, various techniques have been used to form or attempt to form secret or covert or secret images. Unfortunately, as copying and reproduction technologies (such as scanners and printers and computer software for generating images and documents) improve and become available at much lower costs, the security associated with the use of such conventional covert or secret images has come into question.
Some of these techniques have been intended for use with a decoding screen which would reveal a validation message, image, or graphic, while other techniques were intended to render an invalidation message visible when the printed image was photocopied. The later technique for example being commonly used on bank checks.
Some of these techniques relied on ink-based printing and reproduction technologies. Other of these techniques relied on lenticular screens or fly's eye lenses to scramble an image and later reconstruct it. For example, the following United States patents pertain to some techniques for generating or rendering secret messages: U.S. Pat. No. 3,178,993, U.S. Pat. No. 3,524,395, U.S. Pat. No. 3,676,000, U.S. Pat. No. 3,894,756, and U.S. Pat. No. 3,937,565.
Another technique relies on software to initially scramble an image, such as the technique described in U.S. Pat. No. 5,708,717.
Another technique (such as described in U.S. Pat. No. 3,675,948 or U.S. Pat. No. 3,784,289) uses a halftone screen of constant density in which the image area has a shifted angle from the surround area, and uses another constant halftone film of the same frequency as a decoder. Examples of techniques of this type are described in U.S. Pat. No. 3,675,948 or U.S. Pat. No. 3,784,289.
Other related techniques shift the screen frequency in the image areas rather than the screen angle. Examples of this technique are described for example in U.S. Pat. No. 5,197,765 and U.S. Pat. No. 6,000,728.
Another known technique relies on a complex or random binary “code plate” to encode and decode the image. Examples of this technique are described for example in U.S. Pat. No. 3,914,877 and U.S. Pat. No. 4,586,711. A similar technique uses a reference pattern of dots in an apparently random pattern and shifts the dots in the image areas according to the density of the image at that location.
Other approaches have attempted to provide security devices having higher-and-higher resolution in attempt to thwart counterfeiting however, these security techniques and devices are problematic at least in that wet ink or dye based printing techniques have not been able to achieve the resolution or spatial frequency content desired to provide the desired security device features or the desired level of security.
Although these techniques have attempted to provide some measure of secrecy or covertness, they have not been completely successful and therefore problems and limitations remain with such conventional techniques, the security devices produced by such techniques, and the security mechanism or method provided by such techniques.
Therefore, there remains a need for system, method, and device for validating the identity of genuine items whether documents or goods and for identifying counterfeit items on a large scale and desirably at a low per-item cost.